scoutos / prex-0.9.0 / sys / lib / queue.c @ 03e9c04a
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1 | 03e9c04a | Brad Neuman | /*-
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2 | * Copyright (c) 2005, Kohsuke Ohtani
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3 | * All rights reserved.
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4 | *
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5 | * Redistribution and use in source and binary forms, with or without
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6 | * modification, are permitted provided that the following conditions
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7 | * are met:
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8 | * 1. Redistributions of source code must retain the above copyright
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9 | * notice, this list of conditions and the following disclaimer.
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10 | * 2. Redistributions in binary form must reproduce the above copyright
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11 | * notice, this list of conditions and the following disclaimer in the
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12 | * documentation and/or other materials provided with the distribution.
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13 | * 3. Neither the name of the author nor the names of any co-contributors
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14 | * may be used to endorse or promote products derived from this software
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15 | * without specific prior written permission.
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16 | *
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17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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18 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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19 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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20 | * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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21 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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22 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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23 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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24 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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25 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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26 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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27 | * SUCH DAMAGE.
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28 | */
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29 | |||
30 | /*
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31 | * queue.c - generic queue management library
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32 | */
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33 | |||
34 | #include <kernel.h> |
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35 | |||
36 | /*
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37 | * Insert element at tail of queue
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38 | */
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39 | void
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40 | enqueue(queue_t head, queue_t item) |
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41 | { |
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42 | |||
43 | item->next = head; |
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44 | item->prev = head->prev; |
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45 | item->prev->next = item; |
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46 | head->prev = item; |
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47 | } |
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48 | |||
49 | /*
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50 | * Remove and return element of head of queue
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51 | */
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52 | queue_t |
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53 | dequeue(queue_t head) |
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54 | { |
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55 | queue_t item; |
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56 | |||
57 | if (head->next == head)
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58 | return ((queue_t)0); |
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59 | item = head->next; |
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60 | item->next->prev = head; |
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61 | head->next = item->next; |
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62 | return item;
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63 | } |
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64 | |||
65 | /*
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66 | * Insert element after specified element
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67 | */
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68 | void
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69 | queue_insert(queue_t prev, queue_t item) |
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70 | { |
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71 | |||
72 | item->prev = prev; |
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73 | item->next = prev->next; |
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74 | prev->next->prev = item; |
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75 | prev->next = item; |
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76 | } |
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77 | |||
78 | /*
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79 | * Remove specified element from queue
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80 | */
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81 | void
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82 | queue_remove(queue_t item) |
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83 | { |
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84 | |||
85 | item->prev->next = item->next; |
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86 | item->next->prev = item->prev; |
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87 | } |